Signaling systems are critical to the modern communication networks. The good performance of a telecommunication networks depends on the reliable transmission of signaling messages through the telecommunication equipment. A series of specifications and techniques, such as the matured narrow-band No. 7 signaling system, have been introduced in the conventional telecommunication networks to ensure the reliability of a signaling system.
With the gradual maturity of the Internet Protocol (IP) packet-based network technology, it becomes possible to utilize the IP packet-based network to transmit services such as voice service, data service, and multimedia service, etc. This requires combining the IP packet-based network with the conventional circuit switched network for service transmission. In order to achieve the interworking between the conventional circuit switched network and the IP packet-based network, a set of Signaling Transport (SIGTRAN) protocols was constituted by the Internet Engineering Task Force (IETF) for transmitting the signaling of the conventional circuit switched network over the IP network. The MTP3 User Adaptation Layer (M3UA) protocol is a protocol in the set of the SIGTRAN protocols for adaptation of the interface primitive between the Message Transfer Part 3 (MTP3) layer and the upper layer users of the MTP3 layer. M3UA is designed to enable the transparent transmission of messages between the MTP3 (Message Transfer Part 3) and the upper layer users of the MTP3 layer.
The M3UA protocol is used for interworking between SS7 signaling and IP network as well as the transmission of MTP3 user messages over the IP network. The basic application model of the M3UA protocol is as shown in FIG. 1. From the viewpoint of the Telephone User Part (TUP)/ISDN User Part (ISUP)/Signaling Connection Control Part (SCCP) (TUP/ISUP/SCCP . . . ), the Message Transfer Part (MTP) is only a channel for message transmission, i.e., the Message Transfer Part (MTP) is used to ensure the reliable and accurate transmission of user part messages to the user part of the destination signaling point (SP). The MTP includes 3 parts, i.e., Message Transfer Part 1 (MTP1), Message Transfer Part 2 (MTP2), and Message Transfer Part 3 (MTP3). While the M3UA is used for implement user adaptation function of the MTP3.
In the M3UA protocol, several SS7 signaling network management messages are specified as follows:
Destination Unavailable (DUNA): when a related signaling point of an SS7 signaling network has a failure and thus becomes unavailable, the M3UA of the Signaling Gateway (SG) will send the DUNA message to notify the relevant Application Server Process(es) (ASP(s));
Destination Available (DAVA): when a related signaling point of an SS7 signaling network recovers from a failure and thus becomes available, the M3UA of the SG will send the DAVA message to notify the relevant ASP(s);
Destination State Audit (DAUD): this message is used for the ASPs to audit the state of a related signaling point of the related SS7 signaling network to the SG;
Signaling Congestion (SCON): when a related signaling point of the SS7 signaling network is congested, the M3UA of the SG will send the SCON message to notify the relevant ASP(s);
Destination User Part Unavailable (DUPU): when the MTP user part of a related signaling point of the SS7 signaling network becomes unavailable, the M3UA of the SG will send the DUPU message to notify the relevant ASP(s).
As described above, in the specification for SS7 signaling network management messages in M3UA protocol, it is specified explicitly that the signaling gateway (SG) should use the corresponding SS7 signaling network management messages in the M3UA to notify the relevant ASPs whenever the state of a signaling point in SS7 signaling network changes.
FIG. 2 is a schematic diagram showing the application of the SS7 signaling network management messages in M3UA. As shown in FIG. 2, whenever the state of an SS7 signaling point “A” changes, the relevant SS7 Signaling Transfer Point (STP) will notify the SG by using the SS7 MTP3 signaling network management messages, such as Transfer Prohibit (TFP)/Transfer Allowed (TFA)/Transfer Congestion (TFC)/User Part Unavailable (UPU). Then, the SG notifies the relevant ASPs by using the M3UA SS7 signaling network management messages, such as DUNA/DAVA/SCON/DUPU. In this way, the ASPs may learn about the state of the relevant signaling points in the SS7 signaling network quickly. However, though the M3UA protocol specifies explicitly the SS7 signaling network management messages and the corresponding processing schemes as described above, the relevant SS7 signaling points can not learn about the change in the states of the signaling points at the ASP side of M3UA when the states of the signaling points at the ASP side changes, because the M3UA does not notify the SS7 network of the change. Accordingly, an upper layer service user of the signaling points at SS7 side may not know the state change in the signaling points at the ASP side of M3UA, e.g., a failure in a signaling point at the ASP side of M3UA. This may result in a loss of service sent from an SS7 signaling point to the ASP side of M3UA, i.e., the loss of the relevant signaling services. Therefore, the reliability of communication can not be guaranteed.